1. Field of the Invention
The present invention relates to an oscillator circuit and an oscillation stabilizing method for controlling oscillation capability by the number of driven tri-state inverters connected in parallel with a resonator together with inverters.
2. Description of the Related Art
Conventionally, oscillator circuits are widely used for generating a clock serving as a reference for operation of a computer system and so on. The oscillator circuit has a feedback resistor, inverters, and a plurality of tri-state inverters connected in parallel across a resonator and is configured to control the oscillation capability of the resonator by switching the number of driven tri-state inverters out of the plurality of tri-state inverters.
When the oscillation capability of such a conventional oscillator circuit is controlled by the number of driven tri-state inverters, the supply voltage level of the inverter used for oscillation represents a boundary.
However in the case of the conventional oscillator circuit, in which oscillation capability is controlled by the number of driven tri-state inverters using the supply voltage level of the inverter used for oscillation as a boundary, a power supply for the inverter is inevitably varied in voltage level during production. This causes a variation in the control of oscillation capability even after the production. In order to eliminate such variations, it is necessary to adjust each voltage level of the power supply for the inverter, compromising the productivity of the products.
Further, in controlling the oscillation capability, determination is uniquely made by a frequently varying voltage level and the tri-state inverters for controlling oscillation capability are always turned on/off. Thus, a number of variations occur in the oscillation capability and an oscillating operation becomes unstable.
Furthermore, once oscillation is started and if oscillation becomes too unstable to control oscillation capability, no solution is available. When the oscillation output is supplied to various systems including a computer system, the operations of these systems also become unstable.